SMITHSONIAN CONTRIBUTIONS TO THE
EARTH SCIENCES
NUMBER 6
Daniel J. Stanley Distribution of
and Noel P. James EchinarachniuS p
(Lamarck) and
Associated Fauna on
Sable Island Bank,
Southeast Canada
ISSUED
APR 2 7 1971
SMITHSONIAN INSTITUTION PRESS
CITY OF WASHINGTON
1971
ABSTRACT
Stanley. Daniel J., and Noel P. James. Distribution of Echinarachnius parma
(Lamarck) and Associated Fauna on Sable Island Bank, Southeast Canada.
Smithsonian Contributions to the Earth Sciences, number 6, 24 pages, 1971.?A
combined bottom photographic and sampling survey of Sable Island Bank south-
east of Nova Scotia, Canada, reveals locally high densities (to 180 individual/m2)
of the northern sand dollar Echinarachnius parma. Populations of this form are
closely related to texture of the sea floor and generally concentrated on mod-
erately sorted fine to medium sand surfaces. Topography and current regime are
also correlatable factors; depth, time, salinity, and temperature apparently are
not. Sand dollars are second in importance, after current activity, in reworking
surficial sediments, and these organisms modify at least a third of the total Bank
surface in the study area. Bioturbation is particularly intense in the sector north
of Sable Island. Associated epifauna and infauna populations occur in two east-
west trending areas on the Bank north and south of Sable Island. Absence of
conspicuous fauna, save E. parma, in an east-west zone along the crest of the Bank
and near Sable Island results from extremely strong current activity concentrated
in this region.
Official publication date is handstamped in a limited number of initial copies and is recorded in
the Institution's annual report, Smithsonian Year.
UNITED STATES GOVERNMENT PRINTING OFFICEWASHINGTON: 1971
For sale by the Superintendent of Documents, U.S. Government Printing OfficeWashington, D.C. 20402 - Price 45 cents
Daniel J. Stanley
and Noel P. James
Distribution of
Echinarachnius parma
(Lamarck) and
Associated Fauna on
Sable Island Bank,
Southeast Canada
Introduction
The present study was conducted as an outgrowth
of a sedimentological survey (James and Stanley
1968) of the sand-covered, current-dominated shal-
low outer banks of the Nova Scotian Shelf off
southeastern Canada. It is an attempt to evaluate
more precisely than heretofore possible the fauna
likely to affect surficial sediments on a shallow
platform, Sable Island Bank, located far from the
present mainland. It is possible as a result of this
investigation to define the regional distribution
pattern and density of the northern sand dollar,
Echinarachnius parma (Lamarck), and associated
fauna commonly encountered on Sable Island Bank.
Previous investigations (James 1966; James and
Stanley 1968) have shown that this circumboreal
echinoderm is particularly abundant on Sable
Island Bank, the largest of the outer banks on the
shelf. Availability of detailed geographic and hydro-
logic data, together with information on the sedi-
ment regimen, suggested that a study of the benthic
fauna of this area would be particularly profitable.
Data evaluated are derived mainly from bottom
photographs, supplemented by surficial samples
collected at numerous stations distributed over
most of Sable Island Bank and immediately ad-
Daniel J. Stanley, Division of Sedimentology, National Mu-
seum of Natural History, Smithsonian Institution, Washing-
ton, D.C. 20560
Noel P. James, Department of Geological Sciences, McGill
University, Montreal, Quebec, Canada
jacent areas. The present analyses serve, first of all,
to supplement the surprisingly small amount of
quantitative data and field information on this
common sand dollar (Moore 1966). This echinoid
occurs on both margins of northern North America,
in the western North Pacific, and in the western
North Atlantic the known range of E. parma ex-
tends from Cape Hatteras to Labrador and Green-
land (Mortensen 1948). We relate the distribution
of E. parma to such parameters as time of observa-
tion, depth, topography, sediment type, current
regime, and associated fauna. The problem of cor-
relating fauna visually observed on the bottom with
that collected in relatively small bottom grabs is
also considered.
Geographic and Hydrologic Setting of Study Area
MORPHOLOGY.?Sable Island Bank is a sand-
covered platform approximately 250 km long with
a maximum width of 115 km. The 90 m (50 fms)
isobath defines the bank margin (Figure 1). Sable
Island, at approximately 60?W longitude and
43?55'N latitude, is located on the eastern margin
of the Bank, 334 km southeast of Halifax on the
Nova Scotian mainland. Topography and sediments
of the island, a low (relief of 1 to 20 m) east-west
trending arcuate bar of sand flats and dunes about
39 km long and 1.5 km wide, have recently been
described by James and Stanley (1967).
Extremely gentle gradients characterize the bank
top east and south of Sable Island (approximately
1
SMITHSONIAN CONTRIBUTIONS TO EARTH SCIENCES
1:880 and 1:330 respectively) as well as north
(1:280) of the island. Along its steep northern edge,
the Bank is bounded by the Gully Trough, a de-
pression (90 to 210 m deep) characterized by hum-
mocky and dissected topography. This depression
curves southward around the northeast margin of
the Bank and deepens to form the southeast trend-
ing submarine canyon known as The Gully Canyon
(Marlowe 1967). The southeast margin of the Bank
is the boundary between the outer shelf and the
upper continental slope. The outer margin topog-
raphy and sediments have been detailed elsewhere
(Stanley and Silverberg 1969).
GENERAL WATER MASS PROPERTIES.?Water mass
likely to affect sediments and organisms in the
study area is composed of Atlantic water diluted
by 20% coastal water (Hachey 1961) and covers
the outer banks of the Nova Scotian Shelf, includ-
ing Sable Island Bank. Between this "shelf water"
and the Gulf Stream to the south lies a band of
"slope water" having intermediate surface salinities
and relatively low temperatures at middepth. Shelf
water is generally well stratified into three layers
during the summer months and less so during the
winter. The upper layer may be as much as 40 fms
(73 m) thick, with temperatures ranging between
5?C and 20?C and salinities less than 32%O. The
intermediate layer ranges between 17 and 80 fms
(31 to 146 m) in thickness, with temperatures from
0?C to 4?C and salinities between 32%o and 33.5%O.
Bottom water, occupying depths of 50 to 110 fms
(91 to 201 m), has a temperature range from 5?C
to 8?C and salinity gradient from 33.5%O to 35%O.
The intermediate layer is most important in
determining the water characteristics of the outer
banks including Sable Island Bank (Hachey 1961).
The presence of this cold water on the shelf is due
to the large volume of water transported from the
east and northeast by the Labrador Current, and
chilling in situ is a continuous feature, at least
during part of the year. Incursions of slope water
(a mixture of surface, coastal, Gulf Stream, Labra-
dor Current, and upwelling deep Atlantic waters,
as described by McLellan et al. 1953) onto the
Nova Scotian Shelf results is salinity variations on
the outer margin of Sable Island Bank ranging from
33%O to 33.5%O and temperature variations from
5?Cto20?C.
CURRENTS, WAVES, AND TIDES.?The regional distri-
bution of benthic organisms whose feeding and
burial habits make them dependent on the texture
of surficial sediments would almost certainly be
controlled to a considerable degree by water-mass
movement affecting Sable Island Bank. There is
ample evidence that bottom currents do, in fact,
modify the sedimentary cover of the bank top. A
circulatory pattern centered around Sable Island
displays an average rate of drift ranging from 0.11
to 0.15 knots (5.6 to 7.7 cm/sec) (Trites 1958).
This surface circulation pattern varies seasonally
(Bumpus and Lauzier 1965). The northeasterly
and easterly drift along the outer Bank margin con-
stitutes a general off-the-shelf movement and is
consistent except in spring when there is a westerly
drift east of Sable Island. Bottom-circulation pat-
terns in the study area are modified by marked
topographic features including The Gully Canyon
and Sable Island.
In fall and winter, when the Bank top is most
likely to be affected by storms, the number of
waves over 20 feet or more are reported 5% of the
time (Climatological-Oceanographic A tlas for Mari-
ners 1959). In spring the number and size of waves
decrease (waves less than 4 feet in height account
for over 45% of all waves), and in summer waves
over 5 feet in height are rare. Fall and winter are
times of long period, high waves from the west and
northwest. In spring and summer the direction
changes 90 degrees and the waves set from the open
ocean to the south.
Tidal currents are particularly important in
determining the current circulation around Sable
Island (Cameron 1965) and modifying bed forms
on the shallow Bank surface. Cotidal lines, trend-
ing in an ENE-WSW direction across the shelf
(Sverdrup et al. 1942), suggest that the predominant
tidal flow may be NW-SE. Currents do, in fact, tend
to set westward (Canadian Hydrographic Service
1960). The mean range of tides on the bank is 3.7
feet. The ebb stream sets southward at 1.5 to 2
knots (77 to 103 cm/sec) on the submerged termi-
nal bars of Sable Island, and the flood stream runs
0.5 knots (26 cm/sec) less northward {Canadian
Hydrographic Service 1960). Terminal bars of
Sable Island directly affect the flow pattern of tidal
currents in the study area; the morphology of the
terminal bars is, in turn, directly molded by these
currents (James and Stanley 1967).
NUMBER 6
SMITHSONIAN CONTRIBUTIONS TO EARTH SCIENCES
TABLE 1. ?Sample stations on Sable Island Bank, Nova Scotian Shelf
Sample No.
Depth(meters) PositionLongitude Latitude Composition^Gravel
Colour
Sample Equipment
Phleger core Van Veen grab Camera
1
2
1+5
67
89
1011
1213
Ik
15
1$17
18
1920
2122
23
21+<3
26
27
28
2930
31
32
27
38
39
1+0
l+l
1+2
1+3
1+1+
1+6
1+8
50
51
52II
55
56
57
58
59
6o
61
62P
63A
360
3922
23
28
2
20
52
256
175
286
231223
63
1+
128
132
73
1+0
187
50
52
53
20
32
1+1+
52
72
128
120
50
38
20
16
20
26
65
139
121
170
51
29
20
15
1+1+
90
37
90
65
37
38
22
33
38
25
36
20
18
18
59*03.0'
59*15.5'
59*23.5'
59*33-5'
59*38.2'
59*^1-5'
59*31.5'
59*2l+.O'
59*18.0'
59*07-5'
59*15.0'
59*23.0'
59*29.0'
59*37-0'
59*39.0'
59*37-5'
59*32.5'
59*26.5'
59*1+3.0'
59*1+3.0'
59*1+2.0'
59*1+2.0'
59*1+2.0'
59*1+8.0'
59*1+7.5'59*1+8.0'
59*1+7.0'59*^8.5'
59*1+8.0'sample
59*51+.0'
59*5^-0'
59*53-5'
59*5^-0'
59*5^.0'59*51+.0?
60*01.0'
6o?oi.O'
60*00.6'
6o?oi.O'
60*01.0'
60*09.0'
60*07.5'
60*07.5'
60*20.0'
60*07.0'
60*12.0'
60*17.0'
60*20.5'
60*35.0'
60*26.1+'
60*20.0'
60*17.0'
60*11.5'
60*09.5'
60*17.0'
60*32.o?
60*1+3.0*
60*1+7.0'
60*35.0'
60*27.0'
60*19.0'
60*21.0'
i+i+*oo.8f
i+i+*oo.5'
^3*58.5'
l+i+*o6.0'
i+i+*08.0'
l+l+'ll+.O'
l+l+*O2.5'
l+i+*26.5'
l+i+*28.5'
. . ? ^ - ^
l+l+*O2.5'
1+3*58.0'
l+l+*00.0'
l+l+*02.0'
l+l+*20.0'
i+i+*O7.5?
i+i+*O3.5'
1+3*59.0'
1+3*57.5'
^3*57.5'
^3*58.5'
l+l+?10.0'
l+l+*05.0'
^3*5? !o*
l+l+*O2.5'
l+l+?01.0'
1+3*59.0'
I4V05.0'
kk*09.0'
1+3*57.0'
1+3*57.2'
1+3*57.0'
1+3*57-0
1+3*51+.5'
small speck mud
0.00 98.7 1.3
0.00 98.8 1.2
0.00 97.9 2.1
0.00 98.7 1.3
0.00 99.0 1.0
0.00 98.3 1.7
0.00 99.1 0.9
0.00 99.1+ 0.6
96.I+ 2.7 0.8
0.00 38.0 62.0
0.00 72.3 27.7
0.00 60.8 39.2
0,00 97.8 2.2
0.00 99/3 0.7
0.00 89.8 10.2
8.5 85.5 6.0
18.3 80.6 1.1
3-3 95-2 1.5
0.00 35.2 61+.8
0.00 91+.9 5.1
0.00 90.2 9.8
0.00 97.3 2.7
1.0 97-7 1.3
2.2 96.3 1.5
00.0 97.8 2.2
00.0 97.5 2.5
3.7 95.I 1.2
0.00 87.9 12.1
00.0
l+.l
0.7
00.0
00.0
00.0
00.0
00.0
00.0
0.710.9
00.0
00.0
1.900.0
00.0
1.7
71+.7
00.0
19.1
1.0
2.1
00.0
00.0
00.0
00,0
00.0
00.0
00.0
00.0
00.0
00.0
00.0
52.1
90.3
97.0
98.8
98.599.0
99.2
9k. k
77
5.5
2.3
1.2
1.5
1.0
0.8
1.2
1.2
1.3
3 22.0i
1 5-2k 95.6
8 1.
97 A98.5
99.097.5
21+.1
75.
97-
97.
98.7
99.098.8
99.298.9
98.798.8
99.099.0
98.9
.2
0.7
1.5
1.0
0.9
1.2
1.2
5-8
1.6
0.6
l.l
1-3
1.0
1.2
0.8
1.11.3
1.21.0
1.01.1
5Y5/2
2.5Y6.5/1+
2.5Y6.5A2.5Y6/3
2.5Y6.5/I+
2.5Y7/2
2-5Y7/5
2.5Y6.5/I+
2.5Y6/I+
5Y1+/2
5Y1+/2
5Y6/2
2.5Y 6.5/2
5Y1+/2
5Y5/1+
5Y6/1+
2.5Y6.5/8
5Y1+/2
5Y5-5/2
5Y5/2
5Y6/2
2.5Y6/3
5Y6/2
2.5Y6/1+
5Y5/I+
10YR 6/8
5Y1+/2
5Y5A5YI+/3
2.5Y6/I+2.5YU.5/I+
5*5/3.
2.5Y6/32.5Y6/3
.5Y6/3
?5Y6/2
.5Y6/1+
? 5Y1+/1+
7-
2.5Y6/1+
2.5Y6/1+
2.5Y6/3
2.5Y6/2
2,5Y6/i+5/
2.5Y6/1+
2.5Y1+/2
2.5Y5/I+
2.5Y6/1+
5Y5/2
2.5Y6/3
2.5Y6/1+
2.5Y6/1+
2.5Y6/1+
2.5Y6/1+
2.5Y6/1+
2.5Y6/1+
2.5Y6/1+
2.5Y6/1+
2.5Y6/1+
NUMBER 6
TABLE 1. ? Sample stations on Sable Island Bank, Nova Scotian Shelf? Continued
Sample No.
Depth
(meters)
Position
Longitude Latitude
Composition
^Gravel $Sand $Mud Colour
Sample Equipment
Phleger cure VanVeen grab Camera
6465
66
6768
69
70
71
72
73
74
7576
7778
7980
81
82
8384
8586
87
88
89
90
9192
9394
9596
9798
99
100
101
102
103
104
105
106107
108
109
110
111
112
113
114
20
10
38
40
3662
5357
36
20
10
45
59
105
175
50
40
18
18
20
27
46
92
320
54
42
37
10
22
40
46
120
440
80
60
42
40
31
235
99732
230
7654
38
26
20
24
-
102
6o'6o'
60'
60'
60'
60'
60'
60'
6oc
60*
6o?60*
60*
60*
60*
60*
60?
60'
60*60*
60*
6o?60*
59?
59?
59?
59?
59?
59?
59?
59?
59?59*
59*
59*
59?
59?59*
59?
59?
59?
59?
59?59?
59?
59?
59?
59?
59?
59?
59?
'13-5'
'10.0'
'17.0'
'31-51
'43.2'
'35-O'
'26.2'
'18.5'
'14.0'
11.5'
07.5'
12.5'
17.0*
21.0'
07-5'
08.0'
08.0'
O7.O1
07-5'
01.0'
01.0'
01.0'
01.0'
53-5'
52.0'
53-5'
53-5'
55.0'
48.0'
V7.51
^7-5'
48.0'
42.0'
43.01
43.0'
42.5'
36.5;
42.5'
42.5'
29.01
30.0'
14.0'
24.5'
'29-5'
34.o1
38.0'
00.0'
31.0'
16.01
'06.0'
43 57-51
43*57.0'
43*53.5'
43*50.0'
43*46.5'
43*37.0'
43*43.5'
^49,0'
]? >t ?c X, ^'
43*56.5'
43*49.5'
43*40.0'
43*30.0'
43*30.6'
43*45.0'
43*50.0'
43*54.0'
43*41.5'
43*54.5-
43*52.5'
43*49.0'
43*37.5'
43*31.5'
43*46.0'
43*49.0'
43*51.5'
l|.x?SS 0'
43*52.0'
43*49.0'
43*37.3'
43*34.0'
43*41.0'
43*46.0'
43*51.0'
43*52.0'
44*55.0'
43*58.0'
43*59.5'
43*43.5'
43*37.5'
^3*40.0'
43*46.5'
43*51.5-
43*55.5'
43*57.2'
43*58.0'
43*58.0'
43*53.5'
43*50.5'
00.0
2.0
00.0
00.0
00.0
00.0
00.0
00.0
00.0
00.0
00.0
0.8
00.0
00.0
00.0
11.85.6
00.0
00.0
00.0
00.0
00.0
3.5
/
00.0
00.0
00.0
00.0
1.3
00.0
00.0
0.4
00.0
0.9
00.0
00.0
00.0
00.0
12.4
0.00
00.0
00.0
00.0
20.4
00.0
7.5
00.0
00.0
00.0
00.0
00.0
99.9
97.2
98.8
95.6
98.8
98.0
98.4
98.1
98.8
99.0
98.9
96.7
98.0
97-0
9^.5
87.3
92.8
98.8
99-0
96.4
98.5
97.3
95.3/
97.8
96.9
98.1
98.9
97.8
98.0
97.1.
95- h
31.8
97.3
96.3
97.5
98.5
98.6
86.5
98.8
80.5
58.6
94.8
72.2
98.0
90.1
99.1
98.7
98.9
98-9
99.2
1.0
0.8
1.2
4.4
1.2
2.0
1.6
1.9
1.2
1.0
1.1
2.5
2.0
3.0
5.5
0.9
1.6
1.2
1.0
3.6
1.5
2.7
1.2
/
2.2
3.1
1.9
1.1
0.9
2.0
2.9
4.2
69.2
1.8
3-7
2.5
1.51.4
1.1
1.2
19.5
41.4
5.2
2.0
2.4
0.9
1.31.1
1.1
0.8
2.5Y7/4
10YR7/2
2.5Y6/4
2.5Y5/2
2.5Y5A
5Y5/2
5Y5/2
5Y5/2
2.5Y6/2
2.5Y6/3
5Y6/2
5Y5/2
5Y5/2
5Y5/2
5Y5/2
2.5Y6/4
5Y5/2
2.5Y7/2
2.5Y6/2
7-5Y3/2
2.5Y6/2
5Y5/2
5Y5/2
ioyR6/2
7-5Y5/4
5Y5/2
5Y5/1
5Y7/2
2.5Y6.5/4
5Y5/2
5Y5/2
2.5Y5/2
5Y5/1
2.5Y6/4
5Y6/2
5Y5/2
5Y5/2
5*5/2
2.5Y6.5A
2.5Y7/3
5*5/2
5Y5/2
1OY5/1.5
5*5-5/2
5Y6/2
5Y6/2
2.5Y7/3
2.5Y6A
2.5Y6/4
2.5Y6/6
SMITHSONIAN CONTRIBUTIONS TO EARTH SCIENCES
SEDIMENT DISPERSAL.?Bottom currents mold the
surface of Sable Island Bank in response to water-
mass movement of the type described in the pre-
vious section. Large sedimentary features, includ-
ing sand waves and subaqueous dunes in water less
than 40 fms (73 m) deep, show that net current
movement north and south of Sable Island is in
opposite directions: toward the east in the region
north of the island, and toward the west, south of
the island (James and Stanley 1968). Intensity of
current activity increases, as would be expected, in
the shallower water close to the island. This cir-
culatory pattern is confirmed by an independent
examination of the texture and mineralogy of the
sand on the Bank.
Most of the sediment on the Bank surface is
now (or in the recent past) being moved by bot-
tom currents. Winnowing and bypassing of finer
sediment would explain the absence of fine silt and
clay on the Bank surface (Stanley and Cok 1968).
Although much of the Bank is undergoing active
erosion, several zones of probable sediment accum-
ulation are on the Bank margins (shelf-break)
south, east, and northeast of Sable Island (James
and Stanley 1968, their Figure 10).
Methods
A total of 114 bottom grab sample stations were
taken on the Bank and surrounding area during the
period from 5 to 9 May 1965 (Table 1 and Figure
1). The sample grid was planned so that the density
of stations increases toward Sable Island. A Van
Veen type grab sampler, which covers approxi-
mately 0.15 m2 of surface area and when full re-
covers about 20 kg of sediment, was used on 110 of
these stations. Small Phleger cores were collected
at 4 of the deeper stations. Camera lowerings were
made at 32 of these stations with an EG&G bottom
camera rig, below which was suspended at 7.6-cm-
diameter compass for orientation of physical and
biogenic features. The camera was automatically
triggered (not bottom-activated) and photographs
were taken every 12 to 15 seconds while the camera
rig was about 1 to 4 meters above the sea floor. The
camera rig remained near the bottom for approxi-
mately 5 to 10 minutes as the ship drifted on sta-
tion. The direction of drift on station is indicated
by a 25-cm-long vane attached to the compass.
A total of 307 (1 to 30 per station) usable black
and white 35-mm photographs were obtained at
28 of the 32 camera stations. A small clock show-
ing the exact time when photographs were taken
and a number recording the frame sequence, noted
in the data chamber, were also photographed.
Depth of stations ranged from 10 to 250 meters.
Position, water depth, and textural composition of
bottom sediment of each sample station are listed
in Table 1. Complete cruise data and results of
mineralogical analyses of the bottom samples col-
lected at the 114 stations are detailed in James
(1966). Negatives of all photographs are main-
tained in the bottom-photograph collection in the
Division of Sedimentology, National Museum of
Natural History. Data obtained at each of the 28
camera stations are listed in an extensive table
available from the National Oceanographic Data
Center, Washington, D.C. (NODC Accession num-
ber 70-1010). From each usable photograph the
area photographed was calculated and the follow-
ing information recorded: quality of photographs,
presence of compass in photo frame, presence of
ripple marks, sand waves and other current indi-
cators, mottling, bioturbate structures (tracks and
burrows), and fauna. Where one particular species
was abundant (e.g., E. parma or anemones), the
total number of individuals was counted. In the
case of E. parma, apparently stationary, partially
buried and moving individuals were counted sepa-
rately. The occasional white, often overturned, sand
dollar was interpreted to be dead. Finally, the num-
ber of individuals per square meter was calculated.
Sediment Texture and Evidence of Current Activity
Bottom photographs supplement information ob-
tained from the mineralogical and textural anal-
yses (Figure 5). Distinctly different types of sea-
floor microtopography and texture were noted
(Plate 1) : clean sand, generally rippled; shelly
sand with granular texture; silt and silty sand bot-
tom; and sea floor completely modified by burrow-
ing organisms (bioturbation). A light and dark
mottled bottom was observed at a number of sta-
tions. The dark material is almost certainly or-
ganic; the patchy distribution is produced by bur-
rowing organisms and bottom-current activity that
disrupt this bottom veneer.
NUMBER 6
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8 SMITHSONIAN CONTRIBUTIONS TO EARTH SCIENCES
Bottom photographs also provide evidence of
short-term bottom-current activity (Plate 2). Most
useful in detailing current direction are sand rip-
ples noted at 14 camera stations (Figure 2). In one
instance, the predominant orientation of anem-
ones, presumably bending in the current direction
(Station 13), was also noted. The NW-SE trending
crests at Station 82 are those of larger sand waves.
The ripple-crest orientation was recorded at all 14
stations, and the sense of bottom-current move-
ment determined at 8 of these (Figure 2).
In shallow water surrounding Sable Island, the
orientation of ripple marks confirms the circula-
tory pattern described earlier. Northeast of the
island, at Station 59, a NW trend off the Bank is
suggested. Current directions recorded in the head
of The Gully Canyon (Stations 9 and 13) indicate
a movement seaward, generally parallel to the
canyon axis. A predominant downslope current
movement is also noted at the shelf-break near the
head of Sable Island Canyon (Station 18).
It is noteworthy that areas presenting evidence
of strong current activity and those illustrating
mottled sediment are generally mutually exclusive
(Station 55 is an exception). At Station 9, what
appears to be eroded algal matter has been con-
centrated in ripple troughs by bottom-current ac-
tivity.
Echinarachnius parma on Sable Island Bank
POPULATION DENSITY.?The northern sand dollar
Echinarachnius parma (Lamarck) was observed in
13 of 28 camera stations. Where present, the den-
sity ranged to as many as 185 individuals per square
meter (at Station 21). The number of photographs
showing this species varied from 5 to 22 at any
one station. The photo-to-photo variation in den-
sity at each station is depicted on- the histograms
shown in Figure 3.
Immediately apparent is the irregularity of con-
centration (Plate 3) caused by clustering of in-
dividuals. From comparison of the number of
animals counted within the area covered by the
photograph (shown in black on histograms in
Figure 3), it appears that if the area covered ex-
ceeds one square meter, the number counted is
relatively close to the mean for that particular
station (see Stations 8 and 21). Only a few photo-
graphs suffice then to give a reasonably close ap-
proximation to the overall distribution at any one
position on the bank.
It is noteworthy that correlation between individ-
uals photographed at the surface and individuals
retrieved in a small grab at the same station is
poor (Figure 3). Those areas that contain more
than 50 sand dollars per m2 yielded two or more
individuals in the accompanying small Van Veen
grab sample. This low retrieval reflects the small
area covered by the grab but also suggests that not
many sand dollars were buried at the time of the
survey.
REGIONAL DISTRIBUTION.?A chart showing the
distribution and density of E. parma on Sable Is-
land Bank is given in Figure 4. This chart is com-
piled from both bottom photographs and grab
samples (the presence of at least 2 individuals or
more retrieved in a grab sample at a station where
no photos are available indicates the probable
abundance of at least 50 individuals/m2). The
northern sand dollar is present over one third of
the total Bank surface. Highest densities are found
in an arcuate trending belt north of Sable Island
as earlier postulated in a sedimentological study
of the Bank (James and Stanley 1968) . Concentra-
tions of up to 180 individuals per m2 are found
just north of the two terminal submerged bars ex-
tending from Sable Island. High densities (>20/
m2) are rarely found in water deeper than 30 fms
(55 m).
While a large area of relatively few sand dollars
is found on the Bank southeast of Sable Island,
the crests of the island's two submerged terminal
bars, nearshore stations, and the area southeast of
the island appear devoid of sand dollars as well.
Sand dollars do occur, however, in two restricted
areas southeast of the island: (a) a linear NE-SW
trend in shallow water just south of Sable Island's
eastern submerged bar, and (b) at depths of 100
meters on the eastern margin of the Bank adjacent
to The Gully Canyon.
The deepest stations where individuals are en-
countered are near the heads of Sable Island Can-
yon (Station 78, 175 m) and The Gully Canyon
(Station 9, 256 m).
A number of trends were observed in the detailed
photographic analysis. Comparison of sand dollars
with the known compass diameter indicates that the
NUMBER 6
08:17
19:00
(5)
200
100
200
100
11:25
15:16
1
10:10
12:30
(it) 12^25
(111)
... Station number
100
Sequenc eof photo
it* /
E. parma retrieved in grab
LEGEND
FIGURE 3.?Histograms showing photo-to-photo variation in concentration of the northern sand
dollar Echinarachnius parma (Lamarck) (density in m2) as observed at camera and grab stations
on Sable Island Bank. The area covered in each photograph and time of sampling is also
shown.
10 SMITHSONIAN CONTRIBUTIONS TO EARTH SCIENCES
"a
u
&I ?
a *
.S -o
O M
It
18
.2 *-
NUMBER 6 11
6100 30 6000 59?00
S100 5900
SABLE ISLAND BANK
MEAM GRAIN SIZE (M7 )
(After Folk ond Ward , I957) z
I I <O-0 COARSE
\JZZ'i\ 1.0 - 2.0 MEDIUM SAND
|-.?.'.?[ 2.0 - 3.0 FINE SAND IN J UMTS
f-~-1 ^>3.0 VERY PINE SAND
FICURE 5.?Distribution of mean grain size (in <f> units) on Sable Island Bank (after James
and Stanley 1968). Note close relation between the presence of E. parma (see Figure 4) and that
of fine to medium sand grade.
predominant size of E. parma observed in photos
is between 5 and 6 cm. This is in close agreement
with dimensions of this form found off New Eng-
land (Lohavanijaya and Swan 1965). It is difficult
to estimate the amount of movement of individuals
in some photographs due to the absence of re-
worked sand markings. In many cases, however,
partially buried forms and those having left a trail
are noted (Plate 4).
There appears to be no relation between numbers
of individuals and time of day or in the tidal cycle
(Figure 3). Only in a few cases were individuals
found in concentrations such as those observed by
Zenkevitch (1963) in the northwest Pacific. With
the possible exception of Station 56 (Plate 4) in-
dividuals appear to be moving in a random pattern,
confirming the observations of Weihe and Gray
(1968) and Boehmer (1970) on southern United
States species of sand dollars. In areas of high den-
sity this movement is responsible for modifying
physically produced bottom structures, and the
effect of this bioturbation can be seen on Plate 4.
The movement, by rotation and progression, as
described by Parker (1927) in response to feeding
and burying, modifies both rippled and nonrippled
surfaces. The broad, flat, generally arcuate tracks
made by the sand dollars are characteristic and may
be recognized in the fossil record.
At Station 9 (256 m) located in the head of The
Gully Canyon, sand dollars were observed on a
rippled sand bottom in which organic matter, prob-
ably algal detritus, was noted in ripple troughs
(Plate 2f).
Other Epifauna
In addition to E. parma the presence of other or-
ganisms living on the sea floor as noted in bottom
camera stations and grab recoveries include star-
fish, brittle stars, anemones, gastropods, and fish
(hake and cod). Their distribution is shown in
Figure 6 and examples are illustrated in Plate 5.
Starfish [Henricia sanguinolenta (O. F. Miiller)
and others] are found at 8 camera stations from
depths of 20 to over 200 m and appear more nu-
merous north of Sable Island. Brittle stars (Ophi-
12 SMITHSONIAN CONTRIBUTIONS TO EARTH SCIENCES
? 5
? S
o c
a, >~
.2 a,
NUMBER 6 13
-s
w O
^ s
Hl
e3 o
3|
?1
> 2 am
, "3
18
So .2
3 o
14
6100 6000
SMITHSONIAN CONTRIBUTIONS TO EARTH SCIENCES
30 5S[00
61 00 5900
SABLE ISLAND BANK
SORTING
(After Folk and Word,1957)
I I <0.35 V.WELL
0.35-0.5 WELL SORTED
0.5 - 0.71 MODERATar WELL
>0.71 MODERATELY
FIGURE 8.?Regional distribution of sorting of sand on Sable Island Bank. The zones generally
devoid of fauna north and south of Sable Island are very well sorted sands coinciding with
areas of high current activity (Figure 2).
omusium lymani Wyville Thomson at 2 camera
stations and in 3 grab samples), on the other hand,
were not recorded above 90 m. These ophiuroids
appear not to be restricted geographically but are
rather limited to deeper water (for example, Gully
Trough, The Gully Canyon, and outer shelf near
the shelfbreak).
Numerous attached anemones were observed at
6 deep water camera stations (>90 m); north
of Sable Island, at Station 33 (50 m), several ane-
mones were attached to shells. At Station 51 in the
Gully Trough (depth of 146 m) as many as 98
(26/m2) were counted in a single photograph.
Gastropods, including the species Aporrhais oc-
cidentalis, were recognized at 8 camera stations and
recovered in 7 grab samples. These mollusks are
more common north of Sable Island. Gastropods
occur in water deeper than 55 m on the southern
part of the Bank, while north of Sable Island they
are found in depths over 35 m and in even shal-
lower water in the lee of the submerged terminal
bars of the island.
The organisms cited above generally occur to-
gether. The regional distribution of this epifaunal
assemblage occurs in east-west trending zones as
depicted in Figure 4. A belt 34 to 40 km wide that
parallels the shallow crestal axis of the Bank is
generally devoid of conspicuous epifauna.
Infauna
The regional distribution of organisms living
within the surficial sediments cover of Sable Is-
land Bank, evaluated from both photographs and
grab recoveries, is shown in Figure 7. Included in
this assemblage are tubes and polychaetes from
grab recoveries and burrows and tubes observed
in photos. Actual examples are shown in Plate
6. The regional distribution pattern of this assem-
blage is similar to that of the epifauna (Figure
6). The zone devoid of infauna, however, is nar-
rower (12 to 22 km) than that devoid of epifauna
and is more symmetrically oriented along the crest
of the Bank.
Infauna is generally associated with a mottled
sediment surface. Small mounds of light-colored
NUMBER 6 15
sand surrounding burrow openings (Plate 6) are
separated by darker areas, suggesting that this
patchy coloring results, in some cases, from bio-
turbation (i.e., disruption of an originally con-
tinuous dark veneer).
Recognizable pelecypod shells, including Cyrto-
daria siliqua, Pecten magellanicus, and Arctica
islandica, are observed in bottom photographs.
Fragments of shell, or shell hash, are ubiquitous.
Bottom photographs are generally unreliable in
estimating the density of pelecypods because of the
large number of buried individuals. Bottom grab
samples reveal a concentration of shell fragments
in southeast, northeast, and northwest belts trend-
ing away from Sable Island toward deeper water
on the Bank (in James and Stanley 1968, their
Figure 6B) . Shells are also abundant near the south
shore of the island, at ends of both bars, and in
shallow water surrounding submerged offshore
terminal bars.
Discussion
INTERPRETATION OF E. parma DISTRIBUTION.?
There does not appear to be any recognizable cor-
relation between density and regional distribution
of E. parma and time of observation or depth of
water on the Bank. The tolerance of this species
to significantly large seasonal variations of temp-
erature and salinities cited earlier is apparent. The
salinity and temperature of bottom water north and
south of Sable Island are not significantly different
and cannot explain the remarkable faunal differ-
ence in these two regions (i.e., extremely large
number of sand dollars north of the island as op-
posed to low densities south of the island). Preda-
tors that may affect regional distribution are un-
known. The distribution pattern of the northern
sand dollar (Figure 4) can, on the other hand, be
closely related to that of the mean grain size of
sand (Figure 5) which in turn reflects local condi-
tions of bottom current agitation and topography.
The most abundant faunas appear in the fine
(2.0 to 3.0 <f>) and medium (1.0 to 2.0 <?) sand
grades. An exception is Station 8 on the north-
eastern margin of the Bank where high densities
occur on a coarse sand base. Sand dollars are absent
in a large area southeast of Sable Island, an area
covered by very fine (3.0 <?) sand. Sand dollars also
tend to be absent from regions of very well sorted
sand (Figure 8). Areas of well sorted sand on the
Bank crest and shallow region adjacent to Sable
Island coincide with zones of most intense current
activity as shown in Figure 2. Although sand dol-
lars do occur in rippled areas (such as Stations 54,
55, 111) reflecting moderate to intense water move-
ment above the bottom, they are more commonly
encountered on mottled covered bottoms indicative
of somewhat less intense current activity.
The preference for clean sand by E. parma
(Parker 1927) and other species of sand dollars
(Kier and Grant 1965; Bell and Frey 1969) is well
known. The preference for a distinct sand size re-
lated to its burrowing behavior, by Mellita quin-
quiesperforata (Salsman and Tolbert 1965; Bell
and Frey 1969) is also clearly exhibited by E.
parma. This selection of sand that is frequently
mottled and not very well sorted is undoubtedly
related to the detrital feeding habit of E. parma, a
detritus feeder. The apparent relationship of popu-
lation density with intense current agitation should
not be overlooked. As has been suggested by others
(Sokolova and Kuznetsov 1960; Zenkevitch 1963;
Reese 1966), E. parma may obtain some of its food
from suspension. Strong current activity like that
near Sable Island would not be conducive to either
substrate stability or successful suspension feeding.
Furthermore, there is some relation between den-
sity and topography. Like the species Mellita quin-
quiesperforata (Weihe and Gray 1968), E. parma
aggregates in the lee of sand bars, in this case the
large terminal bars of Sable Island. Similarly, the
"clumping" response of this species is similar to
that reported for M. quinquiesperforata (Weihe
and Gray 1968).
Population densities calculated in the study
area are somewhat less variable than those of M.
quinquiesperforata whose concentrations range
from 44 to 821 per m2 (Salsman and Tolbert 1965).
Concentrations of the northern sand dollar on the
Bank are also less dense than those depicted by
Sokolova and Kuznetsov (1960) and Zenkevitch
(1963), whose photographs show extremely high
densities of E. parma, with individuals actually
overlapping.
The observation by Emery et al. (1965, their
Figure 9) that more sand dollars were recovered in
grab samples than were counted in bottom photo-
16 SMITHSONIAN CONTRIBUTIONS TO EARTH SCIENCES
graphs on the continental shelf southwest of the
study area (suggesting that most forms are buried
and not detectable) is not confirmed by the present
study. Our investigation shows that by far more
individuals occur on the surface (as revealed in
bottom photographs) than in grab samples, in-
dicating that most individual sand dollars were
living on or just at the surface at the time of the
survey (May 1965), and that photographs in this
instance are a more valid means of estimating
population (Figure 3).
The distribution of medium and fine moderately
sorted sand bottom selected by E. parma is closely
related to the present near-bottom current regime
on Sable Island Bank. This texture probably traps
an optimum amount of paniculate matter and
grains covered by organic films that tend to sus-
tain high populations. Coarser grain sizes, represent-
ing lag deposits in stronger eroded regimens, are
probably depleted of sufficient organic matter by
abrasion. Finer grain sizes, on the other hand, trap
perhaps too much organic matter thus producing
conditions unsuitable to E. parma. The high num-
ber of sand dollars on the surface may, in fact, be
due to higher concentrations of organic matter in
the sand just below the sediment-water interface.
It has been suggested that the dislike by E. parma
of "foul" (lacking oxygen) sand due to decom-
position of organic matter causes it to remain on
the surface (Parker 1927). At Station 21, an area
containing as many as 180 individuals per m2 on
the surface, a dark malodorous layer of organic
matter was recovered just below the thin light-
colored sand veneer.
The importance of sand dollars as modifiers of
the surficial sediment of Sable Island Bank is clearly
evident. Mellita quinquiesperforata has been
known to level completely a rippled field 6 to 10
cm in height in a single night (Salsman and Tol-
bert 1965). As the activity of E. parma is the same
as this southern species, bioturbation must be
regarded as almost as important as current activity
in molding the microtopography and reworking the
sediment of at least one third of the Bank surface.
DISTRIBUTION OF ASSOCIATED FAUNA.?Other or-
ganisms living on the sea floor show a dominant
distribution pattern that, like that of E. parma,
displays a predominant east-west trend. When abun-
dant, the epifaunal and infaunal associations re-
semble faunas on other shallow outer banks of the
continental shelves of northeastern North Amer-
ica (Wigley 1961; Emery et al. 1965). The area
barren of epifauna (except E. parma) appears in-
dependent of mean grain size (Figure 5) but coin-
cides with the well to very well sorted sand (Fig-
ure 8) and areas of abundant sand ripples and
waves. This would suggest that currents are too
strong in this area for typical northern shelf bot-
tom dwellers. The general absence of Foraminifera
in this barren east-west area adjacent to Sable Island
(James and Stanley 1968) tends to confirm the
above conclusion.
Organisms living within the sediment also require
a reasonably stable bottom and consequently are
not found on the crest of the bank or close to Sable
Island, areas of strongest current activity and mov-
ing sediment. The close association of conspicuous
infauna and mottling (the latter suggesting a more
tranquil current regime) is significant in this
respect.
The northern limit of the infauna zone south of
Sable Island is located closer to the island than that
of the epifauna zone. The narrower barren zone
of infauna would suggest that buried or partially
buried organisms are, as a group, somewhat more
tolerant to current activity than those living on the
Bank surface.
Summary of Observations
This investigation of faunal associations on Sable
Island Bank on the outer margin of the Nova
Scotian Shelf shows the following:
1. The distribution of Echinarachnius parma is
more closely associated with mean grain size and
sorting of the surficial sand cover (in response to
current activity) and with local topography than
with any other measured factors.
2. Densities of E. parma reach to a maximum of 180
individuals per m2 and are highest in moderately
sorted fine- to medium-grained sand.
3. After current activity, sorting and bioturbation
as a result of feeding and movement by E.
parma are the most important factors modifying
the surficial sediment cover of the Bank (more
than one third of the total Bank surface area
including the entire sector north of Sable Is-
land) .
NUMBER 6 17
4. Absence of E. parma from regions of strongest
current activity and also from areas of well
sorted and very fine sand grades is probably re-
lated to feeding and burial habits.
5. Underwater photography applied to northern
sand dollar population studies in environments
such as broad, shallow outer banks proves to be
considerably more reliable than bottom sampling
surveys.
6. The shallow, east-west trending axis of Sable
Island Bank, subjected to intense current actiy-
ity, is devoid of the typical neritic northwest
Atlantic epifauna and infauna. Population of
typical shelf benthic organisms (other than E.
parma) appear in the deeper, somewhat less
agitated waters beyond this shallow axis and,
consequently, their regional distribution shows
a good correlation with sorting independent of
mean grain size.
7. The regional population distribution shows that
conspicuous infaunal assemblages on Sable Is-
land Bank are somewhat more tolerant of strong
near-bottom current agitation and related sedi-
ment movement than are epifauna.
Acknowledgments
Funds to conduct a survey on Sable Island Bank
were provided by the Institute of Oceanography,
Dalhousie University, Halifax, Nova Scotia. We
would like to thank the Captain, officers, and men
of the CNAV Sackville, Dr. F. Medioli, and Dal-
housie University graduate students in the Ocean-
ography Program for their help in collecting bot-
tom samples and photographing the study area.
Our appreciation is also expressed to Drs. D. L.
Pawson and P. M. Kier, Smithsonian Institution,
for critically reading the manuscript. Financial
support to complete this investigation was provided
by Smithsonian Institution Research Foundation
Grant 436330.
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ington.
Zenkevitch, L.
1963. Biology of the Seas of the U.S.S.R. 955 pages. New
York: Wiley.
NUMBER 6 19
PLATE 1.?Variation of sediment texture and microtopographyon Sable Island Bank: a. Station 59, on northwest margin of
Bank, depth 25 m. Coarse, sinuously rippled sand with gran-ules in trough. Some granular material in ripple troughs
may be organic in origin. Wave length of ripple approxi-mately 6 to 12 cm. b. Station 9, in head of The Gully Can-
yon, 256 m. Dark patchy nature of sand bottom referred toas mottling in text. Unlike the sea floor at this station,
mottling and current activity are generally mutually exclu-sive (see Figure 2). c. Station 8, on northeast margin of Bank,
52 m. Echinarachnius parma (Lamarck) on a shelly granu-lar sand bottom. Individual and articulated valves and current
concentrated shell hash are noted, d. Station 13, on eastern
part of Gully Trough, 223 m. Silty sandy sea floor completelymodified (bioturbation) by benthic organisms. Note worm
tube in upper-right corner of photo, e. Station 78, on south-ern margin of Bank near head of Sable Island Canyon, 175
m. Silty sandy (note cloud produced by compass strikingbottom) sediment covered by old rounded ripples, indicating
past current activity. Ripple crests are oriented NNE-SSW.Compass is 7.6 cm in diameter; compass vane is 25 cm in
length. /. Station 51, in Gully Trough between Middle andSable Island Banks, 146 m. Boulders (arrow) on a silty
shelly sand bottom. Note profusion of anemones and otherbenthic organisms at this locality. Boulders are glacially
transported (Stanley and Cok 1968).
20 SMITHSONIAN CONTRIBUTIONS TO EARTH SCIENCES
PLATE 2.?Evidence of current activity on Sable Island Bank:
a. Station 8, on northeast margin of Bank, 52 m. Sand waves(scale provided by Echinarachnius parma) with shell hash
granules and organic detritus concentrated in linear troughs.b. Station 82, on Bank just south of the western tip of Sable
Island, 18 m. Two sets of current ripples on an essentiallysand bottom: predominant sand wave crest orientation of
NW-SE; secondary ripple crests oriented NE-SW. c. Station59, on northwest margin of Bank, 25 m. Straight asymmetric
sand ripples showing predominant current direction toward
the southeast. Compass and E. parma provide scale, d. Station9, in head of The Gully Canyon, 256 m. Sinuous and inter-
ference sand ripples showing somewhat variable current direc-tions, e. Station 78, on southern margin of Bank near head
of Sable Island Canyon, 175 m. Somewhat vague "relict"ripples veneered with silt indicative of current activity some-
time in recent past. /. Station 9, in head of The Gully Can-yon, 256 m. Dark material, possibly of algal origin, concen-
trated in ripple troughs.
NUMBER 6 21
PLATE 3.?Distribution pattern of the northern sand dollar
Echinarachnius parma (Lamarck) on Sable Island Bank:
a. Station 21, on Bank north of eastern margin of Sable
Island, 50 m. High density of northern sand dollar covering
nearly entire sandy sea floor surface. Note starfish below
compass. See also Station 21 in Figure 3. b. Station 21, same
as Figure 1. Much lower concentration of E. parma. c. Station
8, on northeast margin of the Bank, 52 m. Tendency of sand
dollars to cluster on sand wave crests is shown. Shelly and
organic matter and granules are concentrated in troughs.
d. Station 8, same as in Figure 3. Clustering of E. parma in
linear belts trending parallel with sand wave crests, e. Sta-
tion 9, in the head of The Gully Canyon, 256 m. Relatively
low sand dollar population on an asymmetrically rippled
sand bottom. Sand is moving parallel with the major down-
slope trend of canyon. /. Station 33, on margin of Bank north
of Sable Island, 50 m. Population of E. parma on a mottled
and burrowed sand bottom, suggesting tranquil bottom con-
ditions. Note articulated pelecypod valves concave down and
gastropod shell in upper center.
22 SMITHSONIAN CONTRIBUTIONS TO EARTH SCIENCES
PLATE 4.?Bottom markings produced by Echinarachniusparma on the sandy surface of Sable Island Bank: a. Station
21, on margin of Bank north of the eastern sector of SableIsland, 50 m. Evidence of bioturbation produced by the
northern sand dollars on a mottled sand surface. Evidenceof markings produced by rotation and by progression and
combinations of both are noted. Partially buried forms arevisible, b. Station 56, on the Bank adjacent to the submerged
western terminal bar of Sable Island, 22 m. Sand dollarscompletely modifying sand surface of Bank. A possible pref-
erential orientation of individuals moving toward the lowerpart of photograph is suggested, c. Station 88, on Bank south
of Sable Island, 54 m. Close view of shallow parallel trackmade by moving E. parma on sand surface, d. Station 48,
near margin of Bank north of western sector of Sable Island,44 m. Close view of partially buried individuals indicating
movement by rotation. Note starfish Henricia sanguinolenta(O. F. Muller) in right of photograph, and also in a. e. Station
54, on Bank northwest of Sable Island, 37 m. Bioturbationby E. parma on rippled sand bottom. Note curved parallel
track of individual in lower center part of photograph./. Station 22, on Bank north of east terminal bar of Sable
Island, 52 m. Sand dollars on silty bottom covered by darkorganic film. Evidence of burrowing also present.
NUMBER 6 23
PLATE 5.?Association of organisms living on the surface ofSable Island Bank: a. Station 8, on northeast margin of the
Bank, 52 m. Benthic fish resting on sand wave trough. Noteclustering pattern of E. parma. b. Station 48, near margin
of Bank north of western part of Sable Island, 44 m. Largestarfish in upper part of photograph. Note abundant indi-
vidual valves of pelecypods concave up and partially buried.c. Station 86, on margin of Bank south of Sable Island, 92 m.
Abundant brittle star (probably Ophiomusium lymaniWyville Thomson) on mottled sand surface. Sand dollars
give scale, d. Station 16, in Gully Trough north of SableIsland, 128 m. Gastropod (see arrow) on a bioturbate silty
sand bottom. Granular texture is probably organic in origin.e. Station 51, in Gully Trough, 146 m. Large population of
small anemones on gravely silty sand bottom. /. Station 78,on southern margin of Bank near head of Sable Island Can-
yon, 175 m. Large anemones on gently rippled sand. g. Sta-tion 13, in Gully Trough near the head of The Gully Can-
yon, 223 m. Close-up of small anemone on sandy silt bottom.
24 SMITHSONIAN CONTRIBUTIONS TO EARTH SCIENCES
PLATE 6.?Association of organisms living within and on thesediment on Sable Island Bank: a. Station 13, in Gully
Trough near the head of The Gully Canyon, 223 m. Highconcentration of worm tubes on a sandy silt bottom, b. Sta-
tion 13, same as Figure 1. Large number of worm tubes andanemones on a burrowed sandy silt bottom, c. Station 13,
same as Figures 1 and 2. Trails of benthic organisms, prob-ably worms, on burrowed sandy silt bottom, d. Station 33,
on margin of Bank north of Sable Island, 50 m. Small raisedburrows on a mottled shelly sand bottom covered with E.
parma. Reworking by wormlike organisms probably resultedin patchy dark and light-colored bottom. Sand dollars pro-
vide scale. The associated features suggest relatively tranquilcondition on the sea floor, e. Station 8, on northeast margin
of the Bank, 52 m. Partially buried shell, for the most partindividual valves concave down, concentrated in troughs of
sand waves. /. Station 77, on southern margin of Bank, 105m. Large individual valves concave up and partially buried.
Mottled surface produced by burrowing organisms.
?ft U.S. GOVERNMENT PRINTING OFFICE: 1971 O 4II-33O